Much of what the brain learns from experience, including language and sound identification and localization, is acquired through the mechanisms of supervised learning. In supervised learning, plasticity in one network of neurons is regulated or guided by information from another network. Our knowledge of the mechanisms of plasticity has increased tremendously over the past decade. In contrast, our knowledge of the mechanisms that regulate and instruct plasticity remains primitive.The calibration of the auditory system's map of space by the visual system is a well-characterized example of supervised learning. In the barn owl, the site in the auditory pathway where visual signals exert there effects, and the structural and functional changes they cause, have been determined. However, the properties of the instructive signals themselves, and the mechanisms by which they exert their effects, remain a mystery.The proposed research will study the instructive signals that calibrate the auditory space map in the owl. Extracellular electrophysiological techniques will be used to measure responses of instructive neural activity to visual, auditory and cross-modal parameters of stimulation. Pharmacological techniques will be used to determine the neurotransmitters that mediate the instructive signals, and the contribution of neuromodulators to the regulation of auditory plasticity. Anatomical techniques will be used to identify the source of input that gates the instructive activity. Behavioral techniques will be used to study the properties of the instructive signal as it occurs naturally in trained animals. Finally, we will manipulate the instructive signal in an attempt to train neural responses to specific auditory stimuli.This research aims at understanding, in detail, mechanisms that instruct neural plasticity. A thorough knowledge of these instructive mechanisms and the principles by which they operate will add substantially to our understanding of how the nervous system learns from experience. This, in turn, may lead to improved methods for teaching both normal and learning disabled children, as well as to improved therapeutic strategies for maximizing the restoration of function to patients following neurological injury or disease.